1. Field of the Invention
The present invention relates generally to gas turbine engine, and more specifically to turbine rotor blade with root section cooling.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as a large frame heavy duty industrial gas turbine (IGT) engine, includes a turbine with one or more rows of stator vanes and rotor blades that react with a hot gas stream from a combustor to produce mechanical work. The stator vanes guide the hot gas stream into the adjacent and downstream row of rotor blades. The first stage vanes and blades are exposed to the highest gas stream temperatures and therefore require the most amount of cooling.
The efficiency of the engine can be increased by using a higher turbine inlet temperature. However, increasing the temperature requires better cooling of the airfoils or improved materials that can withstand these higher temperatures. Turbine airfoils (vanes and blades) are cooled using a combination of convection and impingement cooling within the airfoils and film cooling on the external airfoil surfaces.
A turbine rotor blade, especially for a blade used in a large frame heavy duty industrial gas turbine engine, includes an airfoil extending from a platform to form a hot gas stream flow path around the blade. To limit stress, a fillet is formed between a transition from the airfoil wall to the platform surface and extends around the leading edge (L/E) of the blade and along both the pressure side (P/S) and suction side (S/S) walls of the airfoil. For the blade trailing edge (T/E) root section, due to migration of the hot gas flow from the blade upper span down to the T/E around the platform region, the blade aft fillet region will experience a hotter gas temperature. Also, at the blade T/E fillet location, a higher heat transfer coefficient or heat load onto the fillet location due to the T/E wake effect will occur. With a higher heat load on the airfoil root section, and a stress concentration issue, the cooling slot for the airfoil T/E root section cannot be located low enough into the blade root section fillet region to provide adequate convection cooling. Cooling of this particular airfoil T/E base region fillet location becomes very difficult. High thermally induced stress is predicted at the junction of the blade T/E and the platform locations. In addition, due to the different effectiveness level of cooling used for the blade and the platform cooling and also because of the mass metal distribution between the blade and the platform, the thermally induced strain during a transient cycle becomes much more severe.